Just back in business with Linux after 5 years and just make login to get more info on my problems:

Well.. I need to design a migration solution from Windows to Open source. initially I have choosen Suse(OS), eDirectory ( Directory services) and GroupWise ( Messaging)

Now the real thing: I need to design messaging for around 5000 users, all these users will access their emails from 3 different sites. I believe they will authenticate centrally from any of the 3 sites.
Briefly I am confused how many post offices I required, where I can use use Clustering for HA, how many Blackberry servers required, etc etc.

Can anyone please help me out in this.. bit urgent